The present disclosure generally relates to displaying content to a user wearing a head-mounted display (HMD) as part of an artificial reality system, and specifically relates to low field myopia for artificial reality systems.
Vergence-accommodation conflict is a phenomenon that occurs to users of virtual headsets such as HMDs. Typically, eyes converge (rotate toward one another) to focus on closer objects and diverge (rotate away from one another) to focus on objects that are further away. The vergence therefore represents the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision. Accommodation is coupled with vergence, and is the process where the lenses of the eyes focus on a close or far away object. During accommodation of an eye, a crystalline lens of the eye changes optical power to maintain a clear image or focus on an object as the object's distance varies. In HMD systems, vergence and accommodation processes are decoupled. In fixed-focused HMD systems, the user's eyes verge to a virtual object, but the accommodation stimulus is incorrect for near objects. The eyes may accommodate to the fixed focus distance of a display in the HMD, conflicting with the verged distance to the virtual object. More often the eyes will accommodate for a near object, which causes image blur since the virtual object distance is fixed. The decoupling of vergence and accommodation processes can cause the user to feel uncomfortable, disoriented, or nauseous. Furthermore, different users wearing the same HMD have different accommodation abilities, e.g., in accordance with an age of a user. In general, older people have less ability to accommodate than younger people, i.e., an accommodative range of older people is smaller than that of younger people. Therefore, it is desirable to design an optical assembly for integration into a HMD that can efficiently drive the accommodation for different users, which would also mitigate the vergence-accommodation conflict.